It is a usual practice in the art to utilise metal door frames of channel like cross-sectional configuration, there being a central door striker portion flanked on its two sides by an inner web and an outer web respectively, each web terminating in a respective end flange which itself terminates in a inturn flange, each inturn flange terminating in an return flange. This invention relates to an assembly of jambs and lintel of a door frame, which also have the above defined cross-sectional shape. The space between the two return flanges is slightly greater than a brick width so that a brick can be interposed between the flanges, and it is usual for the door frame to be tied to brickwork by means of wire or sheet metal ties. Alternatively, a timber frame vertical member or nogging can be positioned between the flanges in the case of a timber frame wall. The inturn flange length is slightly greater than the thickness of plaster, so that the application of plaster or plaster board results in a neat appearance at the junction of the end and return flanges on both sides of the wall.
The joining together of the jamb portions and the lintel portion has always constituted a problem. Early practice was to weld the members together, but this was time consuming and expensive, resulted in heat distortion, and required that the door frame should be transported to site as an assembly. Consequently, efforts have been made to produce a satisfactory interconnection which enables the door frame to be transported to site in a knock-down condition and to be assembled on site. In one proposal, the lintel portion was provided with slots and the jamb portions with tabs which extended through the slots and were folded over, but this resulted in a very flimsy assembly which has not been widely approved by builders. In another alternative, location plates were welded to the contiguous ends of the jambs and lintel portions of the frame but these resulted in the formation of weld marks on the face of the door frame, and in some instances of heat distortion marks, and these also were not of sufficiently high quality to meet with universal acceptance under all conditions.
An object of this invention is to provide a metal door frame assembly wherein the step of assembly can be effected on site, which does not require welding, and which results in a rigid corner connection between the door jamb and lintel portions.